PROJECT SUMMARY The federal Medicare program has invested substantial resources into publically reporting and providing financial incentives for the quality of care in Medicare Advantage (MA) plans using a 5-star rating system, but the validity of these quality ratings remain unknown. Enrollees with worse health status and more complex care needs disproportionately disenroll from MA into Traditional Medicare (TM) and higher rated plans tend to enroll healthier, less socio-demographically disadvantaged beneficiaries. It is unknown whether plan performance ratings reflect the actual provision of better quality of care, or if they are driven by favorable selection. Without a better understanding of the performance of the 5-star rating system, CMS?s current efforts to measure and report plan quality may provide further incentives to avoid high-need beneficiaries, and not reflect the quality of care for these individuals. This study?s long term goal is to identify policy strategies to improve the performance of MA in addressing enrollee needs. Its immediate objective is to identify the relationship between the MA 5- star rating system and the outcomes beneficiaries experience. The central hypothesis is that while there may be improvements in network quality among higher rated contracts, the current incentives and methodologies behind the rating system may not optimize patient outcomes. The study proposes two specific aims: 1) To estimate the impact of improved star ratings on enrollee network quality and enrollee health outcomes, and 2) To evaluate the role of biased disenrollment on subsequent star ratings. To answer both aims this study will use data from the Master Beneficiary Summary file, the Healthcare Effectiveness Data and Information Set (HEDIS), the Health Outcomes Survey (HOS), and the Medicare Consumer Assessment of Healthcare Providers and Systems (CAHPS) for all Medicare Advantage enrollees in 2015 and 2016. MA companies often consolidate low rated contracts into higher rated contracts, moving all enrollees from one contract often into a higher rated one without enrollee selection. In aim one, this study will use this contract consolidation as an exogenous instrument to measure the impact of an improved star rating on an enrollee?s observable and self- reported outcomes. In aim two, this study will use available beneficiary level data to see how different enrollees contribute to a contract?s overall rating, and evaluate the impact of disenrollment among chronically ill enrollees on future year ratings. The proposed work is innovative because it combines a unique set of data that has not been previously linked at this scale and it employs a novel quasi-experimental design to study the effect of star ratings on enrollee outcomes. The proposed work is significant because over 18 million Medicare beneficiaries rely on these star ratings to ensure their plans are providing them with an adequate quality of care. Insights gained from this work will help CMS to improve on the star rating program and the design of incentives in the MA program, to maximize the experience of all patients.